Aircraft control systems incorporating redundant components have become increasingly popular with the passage of time as it becomes more evident that such redundancy contributes substantially to aircraft safety and reliability. A significant amount of development and evolution of such redundant systems and components in aircraft controls has occurred in connection with the design and fabrication of combat aircraft. This fact can readily be appreciated since obviously in this type of aircraft there is not only concern with reliability of the aircraft, but also with its survivability in the face of hostile action against the aircraft occurring at some time during the course of its service life. Coincident with this expectation is also the strong possibility that some damage to the aircraft is likely to occur. In this connection, those familiar with the aircraft arts are also aware of the fact that the intended mission of particular types of combat aircraft often dictate that certain compromises be made in aircraft design to better fulfill the intended mission performance of the particular aircraft, so that the extent of component redundancy, as well as the system complexity, can vary greatly between aircraft types. Notwithstanding this however, the use of the redundant component philosophy has generally been extended to more and more components and systems in aircraft, even to the point where triple and quad redundancy in certain critical areas are no longer unusual so that the survivability and reliability of such aircraft operating in a hostile environment has been considerably enhanced.
Along with the developing complexity and sophistication of redundant aircraft control systems, the number of attendant disadvantages have also proliferated. Among the more obvious of these are the increased costs of manufacture and maintainability that are inherently associated with the elaborate arrangements that have been devised, as well as the sometimes severe weight penalties upon the aircraft, which naturally have a deleterious effect on the performance capabilities of the aircraft. The trends toward increased complexity and sophistication, as well as the measures undertaken to cope with the attendant disadvantages, can be observed as some of the more relevant prior art is noted and discussed.
An indication of the earlier and more primitive attempts at utilizing the redundant philosophy to cope with what may be termed as artificial malfunctions of aircraft control systems caused by such hazards as a student pilot "freezing" at the controls, is disclosed in U.S. Pat. Nos. 1,817,204 and 1,332,345 which disclose variations of aircraft dual control systems which incorporate clutches or similar engageable means that are sensitive to control system jams and permit continued operation of the aircraft control system in the event that the system would otherwise be rendered inoperable.
The U.S. Pat. No. 2,793,503 to Geyer presents a more sophisticated approach and discloses an aircraft pivotal tail assembly having two movable members, each one adapted to be operated by a separate actuator through the use of a roller clutch mechanism. In this disclosure a separate synchronizing mechanism is in communication with each of the respective actuators to effect synchronous operation of the actuators and provide an auxiliary input signal to either of the actuators in the event that the fluid pressure to either actuator is interrupted.
U.S. Pat. No. 3,618,419 perhaps typifies some of the complexity found in a more modern aircraft control system utilizing redundant components and includes a gain control device. In the arrangements disclosed in this patent, a dual input actuator signal is introduced to the gain control device and a single output signal is generated which may be utilized to affect the position of a control member. In this device a comparatively complex whiffletree assembly transmits an output signal under normal operating conditions that is proportional to the sum of the two inputs. In the event of an input failure, a shift means is provided in the linkage to connect the whiffletree and the output to a normally disengaged input to increase the gain of the remaining input signal in order to obtain sufficient signal authority to satisfy the requirements of the system. A disconnect device that is sensitive to a jam failure is also provided to prevent or lock the whiffletree assembly against pivotal movement, and thereby permit the output member to be displaced.
It is helpful to note that the entire body of prior art is principally directed to the utilization of redundant and back-up means to preserve the control authority and signal to the aircraft's movable control members. In other words, the thrust of the prior art development has been directed toward the goal of permitting the continued actuation of the aircraft's movable control members to assure an increased degree of reliability. None of the known prior art appears to contemplate situations where damage to the aircraft's structure or a movable control member could encumber the continued operation of related control members and jeopardize the continued operation of the aircraft.
Accordingly, the present invention provides alternate means for improving the reliability and survivability of an aircraft in the event that a movable control member is incapacitated and may be readily incorporated in a wide variety of aircraft control systems without regard to the extent of component redundancy. The present invention can be introduced into existing systems and will function to complement the reliability and survivability of all such systems with minimal additional weight penalties and virtually no additional disadvantages while adding considerable additional dimension to the aircraft's ability to continue to function after experiencing damage or a malfunction.